Effect of saikosaponins and extracts of vinegar-baked Bupleuri Radix on the activity of β-glucuronidase.

In Traditional Chinese Medicine, liver targeting is usually achieved by coadministration with Vinegar-baked Radix Bupleuri (VBRB), but the mechanism is unclear. In this paper, the influence of VBRB on the activity of β-glucuronidase was investigated and compared with that of saikosaponins. The activity of β-glucuronidase was measured by microplate reader using a 4-nitrophenyl-β-d-glucuronide substrate. The change of 4-nitrophenol content was used to characterize the activity of β-glucuronidase. Bupleurum chinenes were found to be the inhibitor of β-glucuronidase. The inhibition rate of Bupleurum chinenes extracts BC1 (high molecular weight polysaccharides), BC2 (ethanol soluble/water insoluble component), BC3 (extracted by n-butanol, soluble in water), and BC4 (low molecular weight water soluble parts) on the activity of β-glucuronidase was found to be 45.15%, 33.94%, 24.94%, and 34.54%, respectively, after 1 h incubation, with BC1 showing the highest inhibition rate. In contrast, the saikosaponins were demonstrated to be the promoter of β-glucuronidase, with promotion rates of 333.56%, 217.04%, 247.87%, 149.75%, and 92.50% for saikosaponin standard samples A, B, B2, C, and D, respectively, (p<0.05). In conclusion, inhibiting the activity of β-glucuronidase might be one of the reasons why VBRB could influence drug distribution upon its coadministration with other drugs. Since saikosaponins and VBRB extracts have opposite effect, more attention should be paid to the content of saikosaponins in the extracts upon its application.